I like to fry or sautee onions, garlic, chilis, spices (for flavor) and zucchini (the main ingredient); then stir them in a can of chopped tomatoes and simmer for a few minutes. The tomatoes are a way to add a sauce with some thickness that brings all the ingredients together. I want to get close to the texture and consistency, but I'm looking for something else so the dish does not always taste the same.

Is there another vegetable or fruit I could use instead of the tomatoes?

You could use coconut milk and curry-type flavorings (e.g. coriander, cumin, turmeric, galangal, ginger, lemongrass, any type of chili pepper, cilantro), for a very different taste with a somewhat similar texture.

Diced eggplant (aubergine) with some coriander and cumin cooked with the zucchini would also give a very thick sauce consistency. I would cook the eggplant first, until it is quite 'mushy', so as not to overcook the zucchini. If you needed to thin the sauce you could add some stock or a little tomato paste and water.

Top it with a big blob of natural yoghurt at the end if you like that type of flavour.

I like to cook mushrooms with my onions, garlic, and zucchini. I prefer cremini (baby bellas), and I salt them so that they give up a lot of water, which can make things a bit sauc-y. And, of course, you can always mix up the spices.